Date: Sun, 8 Oct 1995 20:18:30 -0700 (PDT) From: Julian Elischer <julian@ref.tfs.com> To: raoul@cssc-syd.tansu.com.au (Raoul Golan) Cc: freebsd-questions@freebsd.org Subject: Re: Question on read syscall on serial port Message-ID: <199510090318.UAA14415@ref.tfs.com> In-Reply-To: <199510090119.LAA07559@kiwi.cssc-syd.tansu.com.au> from "Raoul Golan" at Oct 9, 95 11:19:40 am
next in thread | previous in thread | raw e-mail | index | archive | help
>
> Hello people,
>
> I'm reading from a modem on /dev/cua*. It's a blocking read,
> which means I expect it to wait there until data is available,
> or until the modem loses carrier, or until an error occurs.
>
> At the moment, when the modem loses carrier, the read syscall
> returns a count of 0 data read, but it does not set errno to
> anything (it leaves errno with the same value it had before the
> call).
>
> Is there any way (via an ioctl, a fcntl, an stty(?) or via some
> modem configuration parameter) of having the read syscall put
> some value into errno, such as ENOENT or EIO, when the modem
> loses carrier?
Returning 0 bytes on a blocking call is considered "Notification of EOF"
This is the logical definition of loss of carrier is it not?
you could arange to get a signal possibly.. (I'd have ot go back and look
again)..
>
> I ask this because in the tip code there is a loop
> that exits only once errno is set to these values. This
> means that after the modem's lost carrier my tip session
> fails to exit.
>
> The code is as follows:
>
> /* while some condition */
>
> cnt = read(FD, buf, BUFSIZ);
> if (cnt <= 0) {
> /* lost carrier */
> if (cnt < 0 && errno == EIO) {
> sigblock(sigmask(SIGTERM));
> intTERM();
> /*NOTREACHED*/
> } else if (cnt == 0 && errno == ENOENT) {
> kill(getppid(),SIGUSR1);
> sigblock(sigmask(SIGTERM));
> intTERM();
> /*NOTREACHED*/
> } else {
> printf("%d %d\r",cnt,errno);
> fflush(stdout);
> }
> continue;
> }
> /* end */
>
> Thanks,
>
> Raoul.
>
hmm interesting.. lemme see what psix says.. (if anything...)
nothing in read()
hey are you openning cuax or ttyX?
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199510090318.UAA14415>